This invention relates to a filter process employing a novel thin-walled, extruded activated carbon filter, especially such a filter for use in room temperature water purification processes for removal of sub-micron sized particulates.
Presently used in filtration systems, where particulate removal in the range of 99.5% or more of particulates of a size of 0.5 xcexcm to 0.8 xcexcm, are ceramic candle filters. Such ceramic filters are primarily designed for high temperature applications. However, due to the unavailability of suitable lower cost filters which would still provide the aforesaid degree of sub-micron particulate removal, such ceramic filters have also been employed for filtration or purification processes even when high temperatures are not required, such as at room temperature processes for purification of water. Such use of ceramic filters, when their high temperature properties are not required, results in a greatly increased filtration or purification cost due to the costly nature of such ceramic filters.
Although activated carbon filters have been known and used in water purification processes, it has not heretofore been possible to achieve the aforesaid level of particulate removal employing known activated carbon filters.
It would therefore be desirable that a highly effective thin-walled activated carbon filter be available for use in low temperature filtration and purification processes to replace the unduly expensive ceramic filter units now employed to obtain 99.5% or more removal of particulates of a size of 0.5 xcexcm to 0.8 xcexcm.
It has been discovered that an extruded, thin-walled activated carbon filter tube capable of removing 99.5% or more of sub-micron sized particles of a size of from 0.5 xcexcm to 0.8 xcexcm from water or other liquids at room temperature is provided according to this invention by extruding such a thin-walled activated carbon filter from a composition comprising an essentially homogeneous admixture of:
(a) from about 75% to about 85% by weight activated carbon particles, and
(b) from about 15% to about 25% by weight of a thermoplastic binder powder having an average particle size of from about 5 xcexcm to about 25 xcexcm;
wherein the activated carbon particles comprise:
(a) from about 18% to about 50% by weight of activated carbon particles passing through a 325 mesh screen, i.e. xe2x88x92325 mesh fraction, and
(b) from about 50% to about 82% by weight of activated carbon particles passing through a 200 mesh screen and retained on a 325 mesh screen, i.e. xe2x88x92200 to +325 mesh fraction.
By thin-walled filter tube of this invention it is meant that the activated carbon filter tube has a wall thickness of 0.5 inch (12.7 mm) or less, more preferably 0.3 inch (7.62 mm) or less.
A thin-walled activated carbon filter can be extruded from said composition by the continuous extrusion process disclosed in my earlier U.S. Pat. No. 5,189,092, and will have a density sufficient to remove 99.5% of particles of a size of 3 microns or larger, preferably sufficient to remove 99.5% of particles of a size of about 0.5 xcexcm to 0.8 xcexcm.